Influenza is a major worldwide human pathogen that can cause severe illness and death. Spread of influenza to terminal airways/alveoli with the development of primary viral pneumonia is a life-threatening complication of influenza. Limiting influenza infection of alveolar epithelial cells would be expected to prevent the development of viral pneumonia. In a rodent model we found that alveolar macrophages act to suppress the susceptibility of alveolar epithelial cells to influenza infection by inhibiting the 5 lipoxygenase leukotriene pathway in epithelial cells. Deficiency or dysfunction of alveolar macrophages results in enhanced susceptibility of alveolar epithelial cells to infection and lethal injury. We also found that administration of a leukotriene modifying agent (LMA) at the time of infection mimics the action of alveolar macrophages and suppresses infection of alveolar epithelial cells in the infected animals preventing the development of lethal influenza pneumonia. LMAs are a class of oral medication that inhibit leukotriene formation or action, and are commonly used safe and inexpensive prescription drugs used to treat asthma and allergic rhinitis. If the rodent model findings can be extrapolated to the human, we hypothesize that children and adults with asthma or allergic rhinitis that are treated with LMAs would have a reduced incidence of influenza pneumonia and decreased morbidity and mortality. If these concepts are validated by the proposed study, it would suggest a novel therapeutic approach to decreasing influenza morbidity using an available, inexpensive, oral and safe pharmacologic agent across all ages. Two critical pieces of evidence are needed to move these findings forward into a clinical trial or observational study of empiric use in humans during pandemic influenza: (1) proof of concept that LMAs decrease influenza morbidity in humans, and an estimated effect size, and (2) to complement findings in the rodent model, establishment of the role of human alveolar macrophages and LMAs in regulating the susceptibility of human alveolar epithelial cells to influenza infection in vitro. To address the first aim we plan to conduct a large observational study of children and adults who receive LMAs for asthma or allergic rhinitis to determine the impact on severe influenza events. To address the second aim, we will first establish that the interaction of human alveolar macrophages with human alveolar epithelial cells suppresses infection of alveolar epithelial cells in vitro. We will next demonstrate that treatment of human alveolar epithelial cells with LMAs mimics the effect of alveolar macrophages and reduces the susceptibility of alveolar epithelial cells to influenza infection. Potential Impact: This study aims to explore a novel hypothesis, extending evidence from animal studies that available and safe oral drugs may decrease influenza-related morbidity and mortality and to corroborate the action in human lungs. If these concepts are validated in this study, then an immediately available therapy could be tested in trials, or studied during empiric use in pandemic influenza, to determine if they reduce influenza morbidity and mortality. The results of this study have enormous clinical and public health impact.